Semiconductor device that enables simultaneous read and write/read operation

ABSTRACT

A memory cell array  1  has the arrangement of a plurality of cores, each of which comprises one block or a set of a plurality of blocks, each block defining a range of memory cells serving as a unit of data erase. A core selecting part for selecting an optional number of cores to write/erase data is provided for writing data in memory cells in cores selected on the basis of a write command and for erasing data from selected blocks in cores selected on the basis of an erase command. Thus, there is realized a free core system capable of reading data out from memory cells in unselected cores while writing/erasing data in cores selected by the core selecting part.

This application is a Divisional of Ser. No. 09/987,981 filed on Nov.16, 2001 now U.S. Pat. No. 6,512,693; which is a Divisional of U.S.application Ser. No. 09/563,348 filed on May 3, 2000 now U.S. Pat. No.6,377,502.

RELATED APPLICATION

This application claims benefit of priority under 35 U.S.C. §119 toJapanese Patent Applications No. H11-129321, filed on May 10, 1999, and2000-65397, filed on Mar. 9, 2000, the entire contents of which areincorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a semiconductor device, suchas an electrically rewritable nonvolatile semiconductor memory device(EEPROM flash memory). More specifically, the invention relates to aflash memory system capable of simultaneously executing a data write orerase operation and a data read operation.

2. Description of the Related Background Art

Conventionally, there are various electronic systems wherein a pluralityof memory devices are incorporated. For example, there is an electronicsystem wherein an EEPROM flash memory and an SRAM are incorporated tostore data of the flash memory in the SRAM to exchange data between aCPU and the flash memory via the SRAM and to be capable of directlyrewriting data of the flash memory without passing through the SRAM.

On the other hand, there is recently known a memory system called a readwhile write (RWW) type memory system capable of reading data out from acertain memory region while writing or erasing data in another memoryregion in order to reduce the number of memory chips necessary for thesystem. In order to form a memory device of this type, completelyindependent two memory regions may be simply provided in the memorydevice.

However, if the independently accessed regions are only simply providedin the memory device, there are problems as an RWW type memory system.First, since each of the memory regions independently requires a decoderand a sense amplifier, the layout area thereof is large. Secondly, ifbit lines and word lines are continuously arranged independently everyone of the memory regions, it is not possible to divide each of thememory regions into blocks to read and write data every block. That is,the range of the parallel execution of a data read operation and a datawrite operation is fixed, so that the system can not be applied to manyuses. In order for the system to be applied many uses, a plurality ofkinds of systems having different capacities of memory regions must beprepared.

In a conventional flash memory capable of simultaneously executing adata write or erase operation and a data read operation, a memory cellarray is physically fixed to two banks. For example, considering a32-Mbit flash memory chip, the capacity thereof is fixed so that one ofthe banks has 0.5 Mbits and the other bank has 31.5 Mbits. Therefore,users must newly buy another chip when requiring a different bank size.

In addition, as a circuit construction, dedicated address and data linesare provided every bank. When a write or erase operation is executed inblocks of one of banks, the power supply line of the one of the banks isconnected to a writing or erasing power supply line by a power supplyswitch, and the power supply line of the other bank is connected to areading power supply side. If the opposite operation instruction isinputted, each of the banks is connected to the power supply line on theopposite side by a corresponding one of the power supply switches.

Moreover, a set of sense amplifiers for detecting memory cell data areprovided exclusively for each of the banks. For that reason, although itis possible to execute a read operation from memory cells in one of thebanks while executing a write or erase in blocks in the other bank, itis impossible to simultaneously execute a write or erase operation and aread operation in the same bank.

In addition, since the banks are physically fixed, there is a severelimit to addresses capable of being simultaneously executed, and thesize of each of the banks is also fixed, so that the degree of freedomis very low.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, a semiconductor devicecomprising:

a memory cell array having the arrangement of a plurality of cores, eachof which comprises one block or a set of a plurality of blocks, eachblock defining a range of memory cells serving as a unit of data erase,each of said memory cells being an electrically rewritable nonvolatilememory cell;

a core selecting portion configured to select an optional number ofcores from said plurality of cores for writing or erasing data;

a data writing portion configured to write data in a selected memorycell in a core selected by said core selecting portion;

a data erasing portion configured to erase data from a selected block ina core selected by said core selecting portion;

a data reading portion configured to read data out from a memory cell ina core which is not selected by said core selecting portion; and

a bank setting memory circuit configured to select an optional number ofcores of said plurality of cores as a first bank and to set theremaining cores as a second bank, so as to allow a data read operationto be carried out in one of said first and second banks while a datawrite or erase operation is carried out in the other of said first andsecond banks.

According to another aspect of the present invention, a nonvolatilesemiconductor memory device having a power supply control circuit fordetecting an internal power supply voltage to hold a transition in theinternal power supply voltage at a set level,

wherein said power supply control circuit has a dummy load capacityselectively connected in accordance with a load capacity of an internalpower supply.

According to a further aspect of the present invention, a nonvolatilesemiconductor memory device having a power supply control circuit fordetecting an internal power supply voltage to hold a transition in theinternal power supply voltage at a set level,

wherein said power supply control circuit has a circuit for changing aninternal power supply driving capability in accordance with a loadcapacity of an internal power supply.

According to a still further aspect of the present invention, asemiconductor device comprising:

a plurality of functional blocks, each of which is arranged as a certainlump of circuit functions;

a signal line, arranged in a region of each of said functional blocks,for exchanging a signal between each of said functional blocks and theoutside; and

a common bus line which is provided on a region of said plurality offunctional blocks and commonly for said plurality of blocks and which isconnected to said signal line via a contact.

According to still further aspect of the present invention, anonvolatile semiconductor memory device which has the arrangement of aplurality of cores comprising a set of electrically rewritablenonvolatile memory cells and which is capable of reading data in anoptional core of said plurality of cores while rewriting/erasing data inanother optional core of said plurality of cores, said nonvolatilesemiconductor memory device comprising:

a first data comparator circuit for comparing current of a first dataline, which is selected in a verify read operation for data write/erasein one core of said plurality of cores, with current of a firstreference signal line;

a second data comparator circuit for comparing current of a second dataline, which is selected in a usual data read operation in the other coreof said plurality of cores, with current of a second reference signalline;

first and second current source transistors for allowing a constantcurrent to pass through each of said first and second reference signallines; and

a reference constant current source circuit for driving said first andsecond current sources in parallel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a principal part of a preferred embodimentof a flash memory according to the present invention;

FIG. 2A is a circuit diagram of an address line switching circuit inthis preferred embodiment;

FIG. 2B is a circuit diagram of another address line switching circuit;

FIG. 3 is a circuit diagram of a circuit for deactivating address linesin an unselected core in the preferred embodiment;

FIG. 4 is a circuit diagram of a data line switching circuit in thepreferred embodiment;

FIG. 5 is a circuit diagram of a power supply line switching circuit inthe preferred embodiment;

FIG. 6 is a block diagram of an address buffer in the preferredembodiment;

FIG. 7 is a diagram showing the constructions of a core block registerand a core busy output circuit in the preferred embodiment;

FIG. 8 is a diagram showing the details of a core of a memory cell arrayin the preferred embodiment;

FIG. 9 is a circuit diagram showing the details of a cell array and acolumn gate;

FIG. 10 is a block diagram of an output circuit part in the preferredembodiment;

FIG. 11 is an illustration for explaining the operation of a pluralityof core selections in the preferred embodiment;

FIG. 12 is a diagram showing the construction of a bank construction ROMcircuit for use in a preferred embodiment for a free bank system;

FIG. 13 is a diagram showing the construction of a bank busy outputcircuit in the preferred embodiment;

FIG. 14 is a diagram showing the construction of another bank busyoutput circuit in the preferred embodiment;

FIG. 15 is a diagram showing the construction of a core busy outputcircuit in the preferred embodiment;

FIG. 16 is a diagram showing an example of a bank construction circuitin the preferred embodiment;

FIG. 17 is a diagram showing another example of a bank constructioncircuit in the preferred embodiment;

FIG. 18 is a diagram showing another example of a bank constructioncircuit in the preferred embodiment;

FIG. 19 is a diagram showing another example of a bank constructioncircuit in the preferred embodiment;

FIG. 20 is a diagram showing another example of a bank construction ROMcircuit in the preferred embodiment;

FIG. 21 is a diagram showing the construction of a switching circuit fora core busy output terminal in a preferred embodiment for carrying out ahigh-speed read operation;

FIG. 22 is a diagram showing the construction of an input signalswitching circuit to a power supply line switching circuit in thepreferred embodiment for carrying out a high-speed read operation;

FIG. 23 is a diagram showing the construction of an address buffer inthe preferred embodiment for carrying out a high-speed read operation;

FIG. 24 is a control timing chart for an address buffer in the preferredembodiment;

FIG. 25 is a block diagram of an output switching circuit part in thepreferred embodiment;

FIG. 26 is a timing chart showing a high-speed read operation in thepreferred embodiment;

FIG. 27 is a table showing the relationship between voltages in eachoperation mode of a memory cell;

FIG. 28 is a circuit diagram of a voltage applying system in eachoperation mode of a memory cell;

FIG. 29 is a block diagram of a power supply system in another preferredembodiment;

FIG. 30 is a diagram showing the construction of a power supply lineswitching circuit in the preferred embodiment;

FIG. 31 is a circuit diagram of a charging pump control circuit in thepreferred embodiment;

FIG. 32 is a circuit diagram of a power supply line switching circuit inthe preferred embodiment;

FIG. 33 is a circuit diagram of another power supply line switchingcircuit in the preferred embodiment;

FIG. 34 is a circuit diagram of a regulator type power supply controlcircuit, to which a dummy load is applied;

FIG. 35 is a circuit diagram of another example of a regulator typepower supply control circuit, to which a dummy load is applied;

FIG. 36 is a circuit diagram of a regulator type power supply controlcircuit capable of switching a driving capability;

FIG. 37 is a circuit diagram of another regulator type power supplycontrol circuit capable of switching a driving capability;

FIG. 38 is a diagram showing the construction of a power supply lineswitching circuit as a modification of the power supply line switch ofFIG. 30;

FIG. 39 is a diagram showing a busy output circuit for all of cores;

FIG. 40 is a waveform illustration for explaining a problem in theswitching of a power supply;

FIG. 41 is a waveform illustration for explaining a preferred embodimentof a power supply switching system according to the present invention;

FIG. 42 is a drawing showing an example of a preferred layout of cores;

FIG. 43 is a drawing showing another example of a preferred layout ofcores;

FIG. 44 is a circuit diagram of another preferred embodiment of a powersupply circuit according to the present invention;

FIG. 45 is a graph showing the relationship between the load capacityand driving capability and transition time of a power supply circuit;

FIG. 46 is a graph showing the relationship between the load capacityand driving capability and transition time of a power supply circuit byan external power supply;

FIG. 47 is a layout drawing of a semiconductor device in anotherpreferred embodiment;

FIG. 48 is a layout drawing of a flash memory in another preferredembodiment;

FIG. 49 is a layout drawing of a flash memory in another preferredembodiment;

FIG. 50 is a layout drawing of a preferred embodiment as a modificationof the preferred embodiment of FIG. 49;

FIG. 51A is a layout drawing of another preferred embodiment as amodification of the preferred embodiment of FIG. 49;

FIG. 51B is a layout drawing of a pre-decoder part in the preferredembodiment;

FIG. 52A is a layout drawing of another preferred embodiment as amodification of the preferred embodiment of FIG. 49;

FIG. 52B is a layout drawing of a pre-decoder part in the preferredembodiment;

FIG. 53 is a layout drawing of another preferred embodiment of a flashmemory according to the present invention, which has a redundant block;

FIG. 54 is a diagram showing a typical read system of a flash memory;

FIG. 55 is a circuit diagram of an example of a data comparator circuitfor use in the read system;

FIG. 56 is a diagram showing a write/erase operation in a memory cell;

FIG. 57 is a diagram showing a read system in the preferred embodiment;and

FIG. 58 is a circuit diagram of a constant current source for use in theread system.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the accompanying drawings, the preferred embodiments ofthe present invention will be described below.

(First Preferred Embodiment)

FIG. 1 shows the construction of a flash memory chip using a free coresystem according to the present invention. A memory cell array 1comprises m cores 0 through m−1, each of which has the arrangement of nblocks B0 through Bn−1. Each of the blocks B0 through Bn−1 is theminimum unit of data erase, and has the arrangement of a plurality ofmemory cells. Each of the memory cells is, e.g., a nonvolatile memorycell having a stacked gate structure. Although a core is defined as oneblock or a set of a plurality of blocks, each of the cores comprises nBlocks B0 through Bn−1 in the shown example.

Each of the cores is provided with a decoder circuit 2 including row andcolumn decoders for selecting memory cells, and a local data line 4.

Commonly for all of such cores of the memory cell array 1, a fistaddress bus line (a reading address bus line) 6 a for selecting a memorycell during a data read operation, and a second address bus line (awriting/erasing address bus line) 6 b necessary for an automaticoperation during a data read or erase operation are provided.

Address signals are inputted from the outside by an address inputcircuit provided in an interface circuit 14, and supplied to an addressbuffer circuit 10. From this address buffer 10, a reading address and awriting/erasing address are supplied to the address bus lines 6 a and 6b, respectively, in accordance with an operation mode. The addressessupplied to the address bus lines 6 a and 6 b are selectivelytransferred to the decoder circuit 2 of each of the cores by a switchingcircuit 3 for switching address and power supply lines provided for eachof the cores.

Commonly for all of the cores, a first data bus line (a reading data busline) 7 a used for a data read operation, and a second data bus line (awriting/erasing data bus line) 7 b are provided. A first sense amplifiercircuit (a reading sense amplifier circuit) 11 a used for a data readoperation, and a second sense amplifier circuit (a verifying senseamplifier) 11 b used for a verify read operation during a data write orerase operation are provided so as to correspond to the data bus lines 7a and 7 b, respectively.

By a data line switching circuit 16, the local data line 4 provided foreach of the cores is connected to the reading data bus line 7 a during adata read operation and to the writing/erasing data bus line 7 b duringa data write or erase operation. That is, data of selected memory cellsof each of the cores are read out to the local data line 4, to betransferred to the data bus line 7 a or 7 b by the data line switchingcircuit 16 in accordance with an operation mode, to be detected andamplified by the reading sense amplifier circuit 11 a and the verifyingsense amplifier circuit 11 b, respectively.

The read results of the verifying sense amplifier circuit 11 b are fedto a write/erase control circuit 15. In the write/erase control circuit15, it is determined whether write or erase is sufficient. If it isinsufficient, the control of rewrite or re-erase is carried out.

In addition, commonly for all of the cores, a first power supply line (areading power supply line) 8 a, to which a reading power supplypotential is supplied from a reading power supply 12 a, and a secondpower supply line (a writing/erasing power supply line) 8 b, to which adata writing or erasing power supply potential is supplied from awriting or erasing power supply 12 b, are provided. A voltage boosted bya power supply VCC is applied to the reading power supply line 8 aduring a data read operation, to be supplied to the gate of a memorycell to allow a high-speed read operation. These power supply lines 8 aand 8 b are selectively switched by the switching circuit 3 to besupplied to the decoder circuit 2 of each of the cores.

With the above described construction, even if a data read operation anda data write or erase operation are simultaneously executed, therespective operations can be controlled by the independent address buslines, data bus lines, sense amplifier circuits and power supplycircuits.

Specifically, the operation of simultaneously executing data write anderase operations in the flash memory in this preferred embodiment willbe described below.

Now, a case where a data write operation is carried out with respect tocore 0 and where cell data are read out from another core will bedescribed. If a selecting address signal for core 0 part is inputtedfrom the outside of the chip and if a write command is inputted, thewrite command is determined by the interface circuit 14, and a writeflag rises. By this flag, the address signal of the writing/erasingaddress bus line 6 b is inputted to the decoder circuit 2 of core 0 bythe switching circuit 3 of core 0 part, so that the power supply of thewriting/erasing power supply 12 b is supplied. In addition, the dataline 4 of core 0 part is connected to the writing/erasing data bus line7 b which is connected to the verifying sense amplifier circuit 11 b.

By thus setting the address bus lines, data bus lines and power supplylines, a boosted write voltage is applied to a selected word line incore 0, and a high voltage or a low voltage is applied to bit lines fromthe write control circuit 15 in accordance with write data. Thus, if thememory cells have a floating gate type MOS transistor structure, hotelectrons are injected into the floating gate of a selected memory cellto carry out a data write operation. When one write operation iscompleted, data are read out to be detected by the verifying senseamplifier circuit 11 b. Then, a verify determination is carried out bythe write control circuit 15. If write is sufficient, the operation iscompleted, and if write is insufficient, additional write is carriedout.

During the above described data write operation in core 0, a data readoperation can be carried out in another optional core, e.g., core 1.That is, by the address inputted from the outside, the address signal ofthe reading address bus line 6 a is supplied to the decoder circuit 2 ofcore 1 including a memory cell, from which data are intended to be readout, and the power supply output of the reading power supply 12 a issupplied thereto. In addition, the data line 4 is connected to thereading data bus line 7 a via the switching circuit 16. No data writeand read are carried out. To the decoder circuits 2 of other cores, noaddress signal is inputted, and no data bus line is connected. The dataread out from the selected memory cell of core 1 are detected andamplified by the reading sense amplifier circuit 11 a via the readingdata bus line 7 a. The read data are outputted to the outside of thechip via the interface circuit 14.

In this preferred embodiment, in the above described operation, there isno concept of conventional banks dividing area. That is, it is possibleto optionally read data in any one of cores other than core 0, in whichthe data write operation is being carried out, e.g., in core 2, core 3or core m−1. It is prohibited to input the address of core 0, in whichthe data write operation is being carried out, to execute a data readoperation therein. Thus, if a read demand is made with respect to acore, in which a data write operation is being carried out, a pollingsignal indicating that a write operation is being carried out in theselected core is outputted to inform of this, as will be describedlater.

The operation of simultaneously executing data erase and read operationsis basically the same. For example, a case where a data erase operationis carried out with respect to a selected block of core 0 and where celldata are read out from another core will be described. If a selectingaddress signal for a block in core 0 is inputted from the outside of thechip and if an erase command is inputted, the erase command isdetermined by the interface circuit 14, and an erase flag rises. By thisflag, the address signal of the writing/erasing address bus line 6 b isinputted to the decoder circuit 2 of core 0 by the switching circuit 3of core 0, so that the erasing power supply potential of thewriting/erasing power supply 12 b is supplied. In addition, by the dataline switching circuit 16, the data line 4 of core 0 part is connectedto the writing/erasing data bus line 7 b which is connected to theverifying sense amplifier circuit 11 b.

By thus setting the address bus lines, data bus lines and power supplylines, a negative voltage is applied to all of word lines of a selectedblock of selected core 0 to open bit lines, and a high positive voltagefor erase is applied to source lines to erase data every block. When onedata erase operation is completed, data are read out to be detected bythe verifying sense amplifier circuit 11 b. In the write control circuit15, it is determined whether erase is sufficient. If erase issufficient, the operation is completed, and if erase is insufficient,additional erase is carried out.

During the data erase operation with respect to core 0, if a data readdemand is made with respect to another optional core, a data readoperation is carried out with respect to the core.

Furthermore, while the operation of a NOR memory cell wherein a highvoltage is applied to a source to carry out an erase operation has beendescribed, the operation of a memory cell of a type wherein a highvoltage is applied to the substrate side of a memory cell is the same.In addition, the operation control of a NAND memory cell can be thesame.

The detailed construction of the respective parts of FIG. 1 will bedescribed below.

FIG. 2A shows the construction of the address line switching circuitpart of the switching circuit 3 in each core. The switching circuit 3has two selecting switch groups 31 a, 31 b and core selecting circuits32 a, 32 b for selectively driving the selecting switch groups. The coreselecting circuits 32 a and 32 b are activated by enable signals ENBaand ENBb, respectively. As will be described later, the enable signalENBb is a write/erase enable signal which is “H” when a write or erasecommand is inputted. The enable signal ENBa obtained by inverting theenable signal ENBb by an inverter 11 is a read enable signal which is“H” during a data read operation.

One core selecting circuit 32 b comprises an AND gate G3 activated bythe enable signal ENBb=“H” during a data write or erase operation. Acore selecting address signal of the writing/erasing address bus line 6b is inputted to the AND gate G3, which outputs a core selecting signalSELb=“H” to a selected core. By this core selecting signal SELb, theselecting switch group 31 b is turned on during a data write or eraseoperation. Thus, a writing or erasing address signal ADb of thewriting/erasing address bus line 6 b is supplied to the decoder circuitof the selected core.

The other core selecting circuit 32 a comprises an AND gate G1 activatedby the read enable signal ENBa. To the AND gate G1, a core selectingaddress of the reading address bus line 6 a is inputted. When the enablesignal ENBb is “H”, the enable signal ENBa is “L”, so that the coreselecting signal SELa being the output of the AND gate G1 is “L” whenthe core is selected for a data write or erase operation. At this time,the selecting switch group 31 a remains being OFF. When the core isselected for a data read operation, the selecting signal SELa=“H”, sothat the selecting switch group 31 a is turned on to fed a readingaddress signal ADa of the reading address bus line 6 a to the decodercircuit 2.

That is, in this preferred embodiment, it is prohibited that the writingor erasing core selecting signal SELb and the reading core selectingsignal SELa simultaneously have “H” (glitch) with respect to one core.Thus, when a data write or erase operation is carried out with respectto a certain core, a data read operation can not be carried out in thesame core.

In the core selecting circuit 32 a, there is provided another AND gateG2, to which the same reading core selecting address signal as that ofthe AND gate G1 is inputted. This AND gate G2 is a polling signalgenerator circuit for informing that a data write or erase operation isbeing carried out in a core when a read demand is inputted to the core.To the AND gate G2, a write or erase enable signal ENBb is inputted asan activating signal. Therefore, when the read demand enters the corewherein the write or erase operation is being carried out, the AND gateG2 holds the core selecting signal SELa=“L” while outputting a datapolling signal POL=“H”.

When both of the two core selecting signals SELa and SELb have “L”, thisindicates that the core is unselected. This is detected by a NOR gate G4which outputs a signal DISABLE for deactivating the address line of theunselected core.

FIG. 3 shows a circuit part for forcing the address signal lines and soforth in the unselected core to be grounded by the above describedsignal DISABLE. As shown in this figure, a short-circuiting transistor383 for causing the address lines and data lines 4 to be grounded isprovided in each of the cores. The short-circuiting transistor 383 iscontrolled by the NOR gate G4. When the core is unselected, DISABLE=“H”,so that the short-circuiting transistor 383 is turned on to dischargeelectric charges of all of the address and data lines in the core.

Thus, it is prohibited that the address and data lines are floating inthe unselected core. As a result, it is possible to prevent malfunctiondue to electrostatic noises and so forth, destruction of gate insulatorfilms of the respective parts, destruction of data, and so forth.

The address line switching circuit shown in FIG. 2A uses a systemwherein when both of the two core selecting signals SELa and SELb have“L”, both of the address signal switch groups 31 a and 31 b are turnedoff, and the useless wiring capacity of the unselected core is notconnected to the reading address bus line 6 a and the writing/erasingaddress bus line 6 b.

On the other hand, as shown in FIG. 2B, the address line switch groups31 a and 31 b may be controlled by the enable signals ENBa and ENBb,respectively.

In the system of FIG. 2B, when a write or erase operation is executed inthe core, the address line switch group 31 b is turned on, so that thewriting or erasing address signal ADb of the writing/erasing address busline 6 b is supplied to the decoder circuit 2. When no write or eraseoperation is executed in the core, the address line switch group 31 a isalways turned on, and the reading address signal ADa of the readingaddress bus line 6 a is supplied to the decoder circuit 2. In theunselected core, the disable signal DISABLE is “H”, all of the decodercircuits are unselected, and the data lines are discharged.

In this system, it is not required to turn the address line switch group31 a on during the data read operation, so that it is possible to reducethe switching time to accelerate the data read operation.

FIG. 4 shows a data line switching circuit 16 for switching theconnection between the local data line 4 and the reading data bus line 7a and the writing/erasing data bus line 7 b, taking notice of adjacentcores i and i+1. The group of NMOS transistors Q3 are controlled by thecore selecting signal SELa, which is the output of the core selectingcircuit 32 a, to switch the connection and disconnection between thelocal data line 4 and the reading data bus line 7 a. The group of NMOStransistors Q4 are controlled by the core selecting signal SELb, whichis the output of the core selecting circuit 32 b, to switch theconnection and disconnection between the local data line 4 and thewriting/erasing data bus line 7 b.

That is, when a certain core is in a data write or erase mode, the coreselecting signal SELb(i) is “H” in the core, so that the transistor Q4is turned on to connect the local data line 4 to the writing/erasingdata bus line 7 b. Inversely, when a certain core is in a data readmode; the core selecting signal SELa(i) is “H” in the core, so that thetransistor Q3 is turned on to connect the local data line 4 to thereading data bus line 7 b.

FIG. 5 shows the construction of the power supply line switching circuit41 included in the switching circuit 3 in each of the cores. This, powersupply line switching circuit 41 has level shifters 402 a and 402 bselectively activated by the core selecting circuit 32 b in the addressline switching circuit 3 shown in FIG. 2A, and transfer gates 403 a and403 b controlled by the outputs of the level shifters 402 a and 402 b,respectively. The transfer gates 403 a and 403 b selectively connect thereading power supply line 8 a and the writing/erasing power supply line8 b to the decoder circuit 2.

For example, when the core selecting signal SELb being the output of thecore selecting circuit 32 b is “H”, i.e., when the core is in a datawrite or erase mode, the level shifter 402 b is activated. Thus, thetransfer gate 403 b is turned on by a control signal which is obtainedby shifting the voltage level obtained from the level shifter 402 b, sothat the writing or erasing power supply potential (e.g., a boostedpotential VSW) of the writing/erasing power supply line 8 b is suppliedto the decoder circuit 2. When the core is in a read mode, the coreselecting signal SELb is “L”. At this time, the level shifter 402 a isactivated, so that the transfer gate 403 a is turned on, so that areading power supply potential Vddr of the reading power supply line 8 ais supplied to the decoder circuit 2 via the transfer gate 403 a.

FIG. 5 shows routes for generating the enable signals ENBa and ENBb,which are omitted from FIG. 2A. The data write signal WRITE or erasesignal ERASE obtained by decoding a command in the interface circuit 14is held as information indicating which block in the core has beenselected for write or erase, in a core block register 42 prepared foreach of the cores. On the basis of the core block register 42, a corebusy output circuit 43 outputs an enable signal ENBb=“H” as a busyoutput indicating that the core is in a write or erase mode. The detailsof the core block register 42 and core busy output circuit 43 will bedescribed later.

FIG. 6 shows the construction of the address buffer 10 of FIG. 1. Theaddress buffer 10 has a three-stage structure comprising a first bufferstage 501, a second buffer stage 502, and third buffer stages 503 and504. The first buffer stage 501 has the function of reducing noises ofan address signal supplied from the outside of the chip and ofprotecting the interior thereof. The second buffer state 502 allows thesupplied address signal to directly pass therethrough to be supplied tothe third buffer stage 503, and supplies the address signal to a latchcircuit 505.

In a data read mode, the address signal passing through the secondbuffer stage 502 is converted into a complementary signal in the thirdbuffer stage 503 to be supplied to the reading address bus line 6 a. Ina data write mode, the address signal is held in the latch circuit 505until the operation ends, and the address signal is supplied to thethird buffer stage 504 to be converted into a complementary signal to besupplied to the writing/erasing address bus line 6 b. In the secondbuffer stage 502, a counter 506 is provided for incrementing an addressduring a verify operation in a data erase mode. That is, in an eraseverify operation, the address signal sequentially updated by the counter506 is supplied to the writing/erasing address bus line 6 b via thebuffer stage 504.

FIG. 7 shows an example of the core block register 42 and core busyoutput circuit 43 shown in FIG. 5. The core block register 42 hasregisters R0 through Rn−1, the number of which is equal to the number nof blocks in each of the cores. When the data write signal WRITE orerase signal ERASE is inputted, a flag “H” is held in a registercorresponding to a selected block of a selected core until the operationends. The core busy output circuit 43 has an OR gate 431 for taking anOR of the outputs of the respective registers of the core block register42. When at least one of blocks for write or erase is selected, the ORgate 421 outputs a core busy output (i.e., a write or erase enablesignal) ENBb=“H” in the core busy output circuit 43. In a core whereinwrite or erase is not selected, ENBb=“L” which indicates read enable.

FIG. 8 shows the detailed construction in a core, and FIG. 9 shows theconstruction in a block. As shown in FIG. 9, each of the blocks B0through Bn−1 has a plurality of bit lines BL, a plurality of word linesWL intersecting the bit lines BL, and a plurality of memory cells MC,each of which is arranged at a corresponding one of the intersectionstherebetween. The bit lines BL and the word lines WL are continuouslyprovided in each of the blocks B0 through Bn−1, which serves as a unitof batch erase. A main row decoder 701 for selecting word lines isarranged at the end portion of the arrangement of the blocks B0 throughBn−1, and row sub-decoders 702 for selecting blocks are provided betweenadjacent blocks. A column decoder is arranged in the bit line endportion of each of the blocks B0 through Bn−1. The column decodercomprises column gates 704 for selecting bit lines, and a columnpre-decoder 703.

FIG. 10 shows the construction of an input/output circuit part providedbetween the reading sense amplifier 11 a and the verifying senseamplifier 11 b and the external input/output pad in FIG. 1. OR gates 901and 902 constitute a data polling output circuit for sequentially addingand outputting data polling signals POLi (i=0˜m−2) outputted from thecore selecting circuit 32 a of each of the cores, which has beendescribed in FIG. 2A. An output switching circuit 904 switches the readoutput of the reading sense amplifier circuit 11 a and the data pollingsignal, which are transferred to an output buffer 906.

A data comparator circuit 905 determines output data which areverify-read out by the verifying sense amplifier circuit 11 b during adata write or erase operation. In the case of write, write data suppliedfrom an input buffer 907 are compared with verify read data. If thedetermined result is NG, the determined result is fed to the write/erasecontrol circuit 15, and the control of rewrite is carried out.Similarly, in the case of erase, if the verified result is NG, theresult is fed to the write/erase control circuit 15, and re-erase iscarried out.

In the flash memory with the above described construction, the detailsof the simultaneous execution of a data write operation and a data readoperation, specifically the operation of reading data out from a certaincore while writing data in another core, will be described below.

When a write command is inputted to the chip, a write flag WRITE isoutputted from the interface circuit 14. In response to this internalsignal, in the address buffer 10, an address signal for a memory cell tobe written is latched until the write operation is completed, andsimultaneously, address data latched in the writing/erasing address busline 6 b are outputted. Information of a block including a cell servingas an object to be written is written in a corresponding register of thecore block register 42 as busy information “H”. It is assumed that thecore thus selected is, e.g., core A. In core A, the output circuit 43outputs a core busy output “H” (i.e., enable signal ENb=“H”). Thus, thecore selecting signal SELb of core A is “H”, so that the read demandfrom core A is prohibited.

In addition, by the enable signal ENBb and the core selecting signalSELb, the writing address signal on the writing/erasing address bus line6 b is inputted to the decoder circuit 2 of the selected core A, andsimultaneously, the power supply potential of the writing/erasing powersupply line 8 b is supplied to the power supply of each of the decodercircuits 2, so that the writing/erasing data bus line 7 b is connectedto the data line 4 of core A. Thus, a data write operation is executedin the selected memory cell of the selected core A.

In a write mode, a write load circuit is controlled so as to correspondto write data which are inputted from an I/O pad to be latched in thedata comparator circuit 905 via the data input buffer 907. Meanwhile, ifa data read demand is inputted with respect to a memory cell of a core,e.g., core B, other than core A, a core busy output, i.e., the enablesignal ENBb, is “L” and the core selecting signal SELb is “L” in core B,so that a data read operation is executed. That is, the address signalof the reading address bus line 6 a is supplied to the decoder circuitof core B, and simultaneously, the reading power supply potential issupplied to the decoder circuit. Data of the selected memory cell areread out to the data line 4, and transferred to the reading senseamplifier circuit 11 a via the reading data bus line 7 a to be detectedand amplified therein.

If an address in core A, in which write is being executed, is inputtedas a read address, the data polling signal POL in core A is “H” sincethe enable signal ENBb is “H” in core A. This data polling signal isoutputted to the outside by the output switching circuit 904.

A data read operation can be executed anywhere with respect to data ofmemory cells other than core A, in which the write operation is beingexecuted, so that there is no limit to bank area.

Then, the operation of a circuit for carrying out a data read operationduring a data erase operation will be described. If a data erase commandis inputted, an erase flag ERASE is outputted from the interface circuit14. Thus, busy information “H” is written in a block register serving asan object to be erased. Simultaneously, in the address buffer 10, thecounter circuit 506 is operated to sequentially search all of blockregisters. Then, if it is coincident with the address of core Aincluding the block, in which the busy information “H” is written, thecore selecting signal SELb is “H”. Then, similar to the case of write,the erasing power supply of the writing/erasing power supply line 8 b issupplied to the decoder circuit of core A, and the address of thewriting/erasing address bus line 6 b is supplied thereto, so that thelocal data line is connected to the writing/erasing data bus line 7 b.Thus, an erase voltage is applied to the object block. Thereafter, thememory cell of the object block is incremented by the counter circuit506 to sequentially execute verify.

The read operation during the execution of erase is the same as theabove described operation during the execution of write.

Then, the operation of the data polling circuit will be described. Whena read command is inputted to core A while executing a write or eraseoperation in core A, the enable signal ENBa of core A is “L”, and theselecting signal SELa of core A is also “L”. Thus, the read operation incore A is prohibited. At this time, the data polling signal POL is “H”in core A, and this is outputted to the polling bus line to be inputtedto the output switching circuit 904 as a data polling signal. Inresponse to this signal, the output switching circuit 904 outputspolling data, not the output of the sense amplifier circuit 11 a, to theoutput buffer circuit 906.

FIG. 11 shows the operation in a case where data erase commands aregiven to a plurality of cores A, B and C. In this case, busy informationis stored in the core block registers 42 of cores A, B and C. Thus, thecore busy circuits 43 of cores A, B and C, each of which includes ablock to be erased, output busy information “H”, i.e., an enable signalENBb=“H”, so that the execution of read is prohibited with respect tothese cores to carry out the data polling.

(Second Preferred Embodiment)

With respect to the above described preferred embodiment of a flashmemory according to the present invention, a preferred embodiment of afree bank system constituting a bank having an optional size, accordingto the present invention, will be described below.

In order to realize a free bank system, a bank construction ROM circuit110 shown in FIG. 12 is prepared for each of cores. The bankconstruction ROM circuit 110 constitutes a memory circuit wherein anoptional number of data rewritable nonvolatile memory cells MC1, MC2, .. . , MCn are connected in series. Although the memory circuit maycomprise a single memory cell in principle, the plurality of memorycells are used for safety.

In the bank construction ROM circuit 110, data write is selectivelyexecuted from the outside of the chip via the interface circuit 14. Thatis, when no write is carried out, the threshold Vth of each of thememory cells MC1 through MCn of the bank construction ROM circuit 110 islow. Therefore, by reading this, node A has “L”. When data write isexecuted in all of the memory cells MC1 through MCn to raise Vth, thememory cells MC1 through MCn are turned off, so that node A has “H”.That is, by this write in the bank construction ROM circuit 110, aplurality of cores are divided into two groups, i.e., a group havingnode A of “H” (which will be referred to as “L” group), and a grouphaving node A of “H” (which will be referred to as “H” group).

A bank busy output circuit 120A in the “L” group and a bank busy outputcircuit 120B in the “L” group are formed as shown in FIGS. 13 and 14,respectively. As shown in FIG. 13, the bank busy output circuit 120A inthe “L” group derives a product of “H” output, which is derived byinverting the output of the bank construction ROM circuit 110 by aninverter 122 using an AND gate 121A provided for each of cores, and thecore busy output of the core busy output circuit 43. Then, the sum ofthe outputs of corresponding AND gates 121A in all of other cores isderived by an OR gate 123A. Thus, an “H” output is obtained in the ORgate 123A when any one of cores in banks in the “L” group is in a writeor erase mode (i.e., when the core busy output is “H”). This becomes abank busy output “H” via a transistor Q11.

However, when a write command WRITE or an erase command ERASE isinputted and when a free bank command is inputted, the bank busy outputis outputted. At this time, the output of an AND gate 124A is “H”, sothat the transistor Q11 is turned on. In other cases, the transistor Q11is turned off, and a resetting transistor Q12 is turned on by means ofan inverter 125A, so that a bank busy output terminal is reset to “L”.

As shown in FIG. 14, the bank busy output circuit 120B in the “H” groupderives a product of the output “H” of the bank construction ROM circuit110 and the core busy output of the core busy output circuit 43 by meansof an AND gate 121B. Thus, an “H” output is obtained in an OR gate 123Bwhen any one of cores in banks in the “H” group is in the write or erasemode (i.e., the core busy output is “H”).

FIG. 15 shows a core busy output circuit, provided in each of cores, forbusying all of cores in a bank when a data write or erase operation iscarried out in an optional block in the bank, in a free bank system inthis preferred embodiment. The outputs of the bank busy output circuits120A and 120B shown in FIGS. 13 and 14 are OR-connected via transfergate transistors Q21 and Q22. On transistor Q21 is controlled by asignal which is derived by inverting the output of the bank constructionROM circuit 110 by an inverter 141, and the other transistor Q22 iscontrolled directly by the output of the bank construction ROM circuit110.

Therefore, in the case of the “L” group, the output of the bank “L” busycircuit 120A enters an OR gate 142 via the transistor Q21. On the otherhand, in the case of the “H” group, the output of the bank “H” busycircuit 120B enters the OR gate 142 via the transistor Q22. The registerinformation of the block register of each of cores also enter the ORgate 142. Thus, if any one of banks is busy, core busy outputs “H” areobtained with respect to all of cores belonging the bank. Thus, the dataread of the bank is prohibited, and a data polling signal is outputtedto the outside of the chip.

When the data write or erase operation is completed, the output of theAND gates 124A, 124B shown in FIG. 13 or 14 is “L”, so that the bankbusy output is reset. At this time, the register output of all of theblock registers is also “L”, so that the core busy output of FIG. 15 isalso reset at “L”.

Change from the free bank system to a free core system can be realizedby setting a free bank command entering the bank busy output circuits120A, 120B at “L” and by turning the bank busy output circuits 120A,120B off. The free bank command can be stored by means of, e.g., arewritable ROM circuit. By rewriting this ROM circuit, the free banksystem and the free core system can be freely set.

FIG. 16 shows an example of the whole connection of the bankconstruction circuit. As can be clearly seen from the description withrespect to FIGS. 13 through 15, if the bank busy output of each bank isfed back to the core busy output circuit 43 of each core, the cores ofthe “H” group can be linked to each other to form one bank, and thecores of the “L” group can be linked to each other to form another bank.

The operation of the simultaneous execution of data write or erase anddata read in each bank is basically the same as that in the free coresystem.

In this preferred embodiment, by the data rewrite in the bankconstruction ROM circuit 110, it is possible to optionally change thebank constructions of the “L” and “H” groups.

(Third Preferred Embodiment)

FIG. 17 shows a preferred embodiment as a modified embodiment of thebank construction circuit of FIG. 16. In the construction of FIG. 16,there are arranged a plurality of busy signal lines entering the ORgates 123A, 123B of the bank busy output circuits 120A, 120B. On theother hand, in FIG. 17, a single busy signal line 163 and a single busysignal line 164 are provided in each bank. These busy signal lines 163,164 are provided with PMOS transistors Q43, Q44 for pull-up, and set at“H” level when no bank busy is outputted. In each core, transistors Q41,Q42 controlled by the outputs of the AND gates 121A, 121B are providedbetween the busy signal lines 163, 164 and the ground, respectively.Therefore, when the bank is busy, the transistor Q41 or Q42 is turnedon, so that the signal line 163 or 164 has “L”. This is inverted byinverters 161, 162, so that any one of the bank busy output circuits120A, 120B outputs a bank busy output “H”.

According to this preferred embodiment, the number of signal lines canbe greatly reduced.

(Fourth Preferred Embodiment)

FIG. 18 shows a preferred embodiment as a modified embodiment of thebank construction circuit of FIG. 16. In this preferred embodiment, theOR gates 123A, 123B in FIG. 16 are distributed in each core part toarrange OR gates 171, 172. Also according to this preferred embodiment,the number of signal lines can be reduced. In the preferred embodimentshown in FIG. 17, current consumption occurs in the transistors Q41,Q42, whereas in this preferred embodiment, such current consumption doesnot occur.

(Fifth Preferred Embodiment)

FIG. 19 shows a preferred embodiment wherein the bank constructioncircuit shown in FIG. 16, 17 or 18 is modified to provide a bank readoutput circuit 391. In the preferred embodiment shown in FIG. 16, 17 or18, each bank busy output is fed back to the core busy output circuit ofa core constituting the bank to realize a free bank system. On the otherhand, in this preferred embodiment, no bank busy information is fedback, and each bank busy information is compared with each bank readinformation, which is obtained by the bank read output circuit 391, onthe output side, to detect a read address input (read information) to abank in a data write/erase mode to carry out the data polling toapparently realize a free bank system.

That is, when the core busy output circuit 43 selects the core as a corein a data write/erase mode to output a core busy output ENBb=“H”, a bankbusy output is obtained in any one of AND gates G17, G16 in accordancewith information on the “H” and “L” groups determined by the bankconstruction ROM circuit 110. These outputs are added to the bank busyoutputs of other cores by OR gates G19, G18.

In addition, an AND gate G20 detects the coincidence of the output ofthe core busy output circuit 43 with a core selecting signal from thereading address line. When the core is in a data write/erase mode andwhen a subsequent read demand is made, a data polling output “H” isoutputted.

On the other hand, in the bank read output circuit 391, a core selectingsignal from the reading address bus line is detected by an AND gate G11.When the output of the AND gate G11 has “H”, i.e., when read informationis outputted, bank read information “H” is outputted to any one of ANDgates G12, G13 in accordance with information on the “H” and “L” groupsfrom the bank construction ROM circuit 110. These are also added to theread information in other cores by OR gates G14, G15, to be transferredto an output stage.

In the output stage, the coincidence detection of the bank busyinformation with the read information in the “H” group, and thecoincidence detection of the bank busy information with the readinformation in the “L” group are carried out by AND gates G23, G24,respectively. The outputs of the AND gates G20, G23 and G24 are summedup by an OR gate G22. Thus, when one bank is in a data write or erasemode and when a read demand enters this bank, data polling is carriedout, so that it is possible to substantially obtain a free bank system.

(Sixth Preferred Embodiment)

FIG. 20 shows a preferred embodiment as a modified embodiment of thebank construction ROM circuit 110. In this preferred embodiment, thebank construction ROM circuit 110 is formed using a fuse FS. Also inthis case, by selectively cutting the fuse FS after a memory chip isformed, it is possible to realize a bank construction of “L” and “H”groups having an optional size. However, in this system, if once thebank construction is set, the bank size can not be changed, and the freebank system can not be changed to a free core system.

(Seventh Preferred Embodiment)

A preferred embodiment for rapidly carrying out a data read operation inthe flash memory described in each of the above described preferredembodiments will be described below.

In a high-speed data read mode, the reading address bus line 6 a, thereading data bus line 7 a, and the reading sense amplifier circuit 11 aconnected to the data bus line 7 a are used as a first data read path.In addition, the writing/erasing address bus line 6 b, thewriting/erasing data bus line 7 b and the verifying sense amplifiercircuit 11 b connected to the data bus line 7 b are used as a seconddata read path. These data read paths are operated so as to overlap eachother by a half period, to carry out a high-speed data read operation.

In order to realize such a high-speed read operation, it is required tochange the core selecting circuits 32 a, 32 b of each core shown in FIG.2, the power supply line switching circuit 41 shown in FIG. 5, theaddress buffer 10 shown in FIG. 6, the output switching circuit 904shown in FIG. 10, and so forth.

First, if a high-speed read commend is inputted, the terminals for theenable signals ENBa, ENBb entering the core selecting circuits 32 a, 32b of each core are electrically disconnected from the core busy outputcircuit 43 by NMOS transistors QN211, QN212 as shown in FIG. 21, so thatpull-up PMOS transistors QP21, QP22 are turned on to be fixed in “H”state. Simultaneously, as shown in FIG. 22, by the high-speed readcommand, an NMOS transistor QN221 on the path for the power supplyswitching circuit 41 of the core selecting circuit 32 b is turned off,and a short-circuiting NMOS transistor QN222 is turned on, to be fixedin “L”.

Thus, the core selecting signals SELa, SELb of all of cores aredetermined by only the core address signals of the address bus lines 6a, 6 b, and the decoder power supply is always connected to the readingpower supply line 8 a.

The address buffer 10 is changes so that the part of the second bufferstage 502 shown in FIG. 6 has two sets of latch circuits 191, 192 asshown in FIG. 23. These latch circuits 191, 192 are provided foralternately latching the address of a memory cell to be read, by timingsignals PULSEb, PULSEa to supply the address to the address bus lines 6a, 6 b.

In order to generate the timing signals PULSEa, PULSEb, there areprovided a clock generating circuit 193 for detecting address transitionto generate a clock CLK, and a counter circuit 194 for counting theoutput of the clock generating circuit 193 to produce a count outputCOUNT having a double period. In addition, AND gates 196, 197 activatedby the clock CLK are provided. The count output COUNT is inputteddirectly to the AND gate 196, and the count output COUNT is inverted byan inverter 195 to be inputted to the AND gate 197, so that timingsignals PULSEa, PULSEb shifted by a half period from another aregenerated.

FIG. 24 is a operation timing chart for the circuit of FIG. 23. As shownin this figure, a clock CLK is generated in synchronism with an inputaddress. In response thereto, timing signals PULSEa, PULSEb aregenerated. By the latch circuits 192, 192 by the timing signals PULSEa,PULSEb, an address is alternately transferred to the address bus lines 6a, 6 b.

The outputs of the latch circuits 191, 192 are provided with thirdbuffer stages as shown in FIG. 6. In this case, an output comparatorcircuit (not shown) is provided between the latch circuits 191, 192 andthe third buffer stages. This is provided for outputting a data pollingsignal without outputting a subsequently inputted address to the thirdbuffer stages when the input addresses enter in the same core. By such adata polling, it is possible to prevent circuit destruction andmalfunction due to the simultaneous selection of the same core.

In addition, as shown in FIG. 25, it is required to provide an outputswitching circuit 210 for switching the output of the verifying senseamplifier circuit 11 b and the output of the reading sense amplifiercircuit 11 a. This output switching circuit 210 is controlled by theclock CLK to alternately switch the output of the verifying senseamplifier circuit 11 b and the output of the reading sense amplifiercircuit 11 a to output data to the output buffer circuit.

FIG. 26 is a timing chart for a high-speed read operation in thispreferred embodiment. Read data obtained by the respective senseamplifier circuits 11 a, 11 b while being shifted by a half period inresponse to addresses {circle around (1)}, {circle around (2)}, . . .shown in FIG. 24 are controlled by the clock CLK to be outputted as ahigh-speed read output Dout.

According to the system in this preferred embodiment, it is possible torealize a high-speed data read operation capable of reading data torandom addresses by the half of a usual period. However, read to thesame core is prohibited, and data polling is carried out. In addition,since the address cycle from the outside of the chip is doubled insideof the chip, output data are shifted by one cycle. However, if such asystem is recognized to form a system, it is possible to realize ahigh-speed chip access.

Furthermore, the high-speed read command is controlled by, e.g., acommand from the outside of the chip. Alternatively, if it is used as anOTP, a high-speed command may be controlled by whether data are writtenin a data memory circuit comprising ROM cells provided in a chip.

A preferred embodiment of a power supply system of a flash memoryaccording to the present invention will be described below. Before thedescription thereof, the relationship between operation voltages of amemory cell is shown in FIG. 27. During a data read operation, a boostedpotential 5V is applied to the gate (word line) of the memory cell, 1Vis applied to the drain thereof, and 0V is applied to the sourcethereof, so that the current passing through the cell is detected by asense amplifier. During a data write operation, a boosted voltage isapplied to the word line, 5V is applied to the drain, and 0V is appliedto the source, so that hot electrons generated between the drain and thesource are injected into the floating gate. During a data eraseoperation, the drain is open, −7V is applied to the word line, and 5V isapplied to the source, so that the high voltage between the floatinggate and the source causes electrons to be emitted by the FN tunneling.

FIG. 28 schematically shows a voltage applying system during read, writeand erase operations with respect to a memory cell, The word line of thememory cell is driven by a row decoder. By a switch SW1, the highpotential level of the row decoder is connected to Vddr=5 during a readoperation, and VSW=8V during a write operation. By a switch SW3, the lowpotential level of the row decoder is connected to VBB=−7V during anerase operation. Thus, to the word line, i.e., the gate G, of the memorycell, 5V, 8V and −7V are applied during the read, write and eraseoperations, respectively.

During a read operation, the drain D of the memory cell is connected toa sense amplifier, so that 1V is applied thereto via the senseamplifier. During a write operation, the drain D of the memory cell isconnected to a load LOAD, so that 5V is applied thereto via the load.During an erase operation, the drain is open.

To the source S of the memory cell, 5V is applied during an eraseoperation. In other modes, the source S of the memory cell is grounded.The load LOAD is connected to Vdd and a charging pump output Vddp via aswitch SW2.

(Eighth Preferred Embodiment)

FIG. 29 shows an example of a reading power supply 12 a and awriting/erasing power supply 12 b. The reading power supply 12 a and thewriting/erasing power supply 12 b generates a desired level on the basisof the output of a reference potential generating circuit 320 using,e.g., a band gap reference (BGR) circuit. In this case, there are thefollowing three cases in a method for generating a desired level.

Case (1): A charging pump circuit is on-off controlled.

Case (2): The output obtained in case (1) is further controlled by aregulator.

Case (3): The output obtained in case (1) and a constant potential(e.g., VSS) are switched.

In FIG. 29, the reading power supply line 12 a, and the power supplyline {circle around (2)} of the three power supply lines 8 b{circlearound (1)}˜{circle around (3)} of the writing/erasing power supply 12 bcorrespond to case (1). That is, the reading power supply 12 a and thewriting/erasing power supply line 6 b{circle around (2)} comprisecontrol circuits 322, 324 b for on-off controlling a charging pumpcircuit, and charging pump circuits 323, 325 b controlled by thecircuits 322, 324 b. In these power supply circuits, if the power supplylevel is a desired level or less, the charging pump circuits are driven,and if the power supply level reaches the desired level, the chargingpump circuits are stopped.

The writing/erasing power supply line 8 b{circle around (1)} correspondsto case (2), and has a control circuit 324 a for on-off control, acharging pump circuit 325 a controlled by the circuit 324 a, and aregulator control circuit 326 for controlling the output level of thecharging pump circuit 325 a. Specifically, this is used for carrying outan automatic data write operation for repeating write and verifyoperations using a write voltage of 8V and a verify reading voltage of6.5 V, and the regulator control circuit 326 is used for such a voltagecontrol.

The writing/erasing power supply line 8 b{circle around (3)} correspondsto case (3), and has a control circuit 324 c for on-off control, acharging pump circuit 325 c for negative potential controlled by thecontrol circuit 324 c, and a switching circuit 327 for switching theoutput of the charging pump circuit 325 c. The switching circuit isprovided for outputting VSS when the charging pump 325 c is notoperated.

The above described three systems of writing/erasing power supply linesare activated by an auto control signal, which is outputted from a writestate machine 321, in accordance with write/erase operation modes.

FIG. 30 shows the construction of a power supply line switching circuit16, which is a part of an address line switching circuit 3 for switchingthe power supply lines of the power supply circuit of FIG. 29 inaccordance with an operation mode to supply a power supply line to eachcore. As shown in this figure, the power supply line switching circuit16 comprises three switching circuits SW1 through SW3. These switchesSW1 through SW3 are controlled by a writing/erasing enable signal ENBb,which is the output of a core switch control circuit 250 in this example(specifically, corresponding to the core busy output circuit 42 shown inFIGS. 5 and 7).

FIG. 31 shows an example of a control circuit 324 (322 is the same) foron-off controlling the charging pumps shown in FIG. 29. An operationalamplifier circuit 331 is used for detecting the output VCP, which isobtained by the charging pump circuit 323, 325 and so forth, by avoltage divider circuit comprising resistors Rload and Rref and forcomparing the output VCP with a reference voltage Vref. The output ofthe operational amplifier circuit 331 is derived from a buffer 322 as acharging pump enable signal CPENB.

FIG. 32 shows an example of switching circuits SW1, SW2 for switching areading power supply, which is obtained in the reading power supply line8 b, and a positive writing/erasing power supply which is obtained inthe writing/erasing power supplies 8 b{circle around (1)}, {circlearound (2)}. A level shifter 230 controlled by an enable signal SWENB(corresponding to the enable signal ENBb in FIG. 29) generates a controlsignal having a voltage level, which is shifted from VCC system to avoltage between the positive high potential power supply VCP from thecharging pump circuit and VSS. This control signal on-off controlsoutput stage transistors QP3, QN3 and QP4 via inverters 233, 234. Thatis, if the output of the inverter 233 has “H”, the NMOS transistor QN3and the PMOS transistor QP4 are turned on to output a read power supplyVddr. If the output of the inverter 233 has “L”, the PMOS transistor QP3is turned on to output a boosted power supply VSW.

FIG. 33 shows an example of a switching circuit SW3 for switching anegative power supply potential VBB obtained in the writing/erasingpower supply line 8 b{circle around (3)}, and the ground potential VSS.A level shifter 240 controlled by an enable signal SWENB generates acontrol signal having a voltage level shifted from VCC system to avoltage between an intermediate potential power supply VSW and thenegative power supply potential VBB. This control signal controls outputstage transistors QN17, QN18 and QP15 via inverters 243, 244. That is,if the output of the inverter 243 has “H”, the NMOS transistor QN17 isturned on to output a negative power supply VBB. If the output of theinverter 243 has “L”, the PMOS transistor QP15 and the NMOS transistorQN18 are turned on to output VSS.

In the power supply switch control system shown in FIG. 30, the powersupply of each core is fixed to the reading power supply or thewriting/erasing power supply during a data write or erase operation.Therefore, in the case of a free bank system wherein a write/eraseoperation is carried out over a plurality of cores, the power supplytransition can be carried out regardless of the address switching ofcore selection. However, in the free bank system, the capacity driven bythe power supply varies in accordance with the number of selected coresof a block register. Therefore, the power supply transition time variesin accordance with the number of selected cores, or there is thepossibility that the power supply transition oscillates when the numberof selected cores is small.

As methods for solving such a problem, the following two methods areconsidered. First, the magnitude of the load of a power supply controlcircuit (regulator) is held to be substantially constant regardless ofthe number of selected cores. Specifically, a dummy load capacityselectively connected to a power supply control circuit is provided, andan internal power supply voltage or an external power supply voltage isdetected to control the load capacity in accordance with the detectedresults. Secondly, the driving capability is switched in accordance withthe number of selected cores. Also in this case, specifically, aninternal power supply voltage or an external power supply voltage isdetected to switch the driving power in accordance with the detectedsignal.

Specifically, such a preferred embodiment of a voltage control circuitaccording to the present invention will be described below.

(Ninth Preferred Embodiment)

FIG. 34 shows a preferred embodiment of a voltage addition type powersupply control circuit according to the first method. A regulator body260 has PMOS transistors QP21, QP22 and NMOS transistors QN21, QN22,which constitute a differential circuit for level-controlling andderiving the output VCP of a charging pump circuit, and two operationalamplifiers OP1, OP2 for controlling the differential circuit inaccordance with the output level. The output level is monitored as adivided voltage output of resistors Rload and Rref, and fed back to theoperational amplifiers OP1, OP2 to obtain a predetermined voltage level.The resistor Rload can be switched by a switch 261, which is controlledby mode signals MODE1 through MODE4, so that a required power supplylevel is controlled.

In this preferred embodiment, a plurality of dummy core capacities C areoptionally selected to be connected to the output terminal of such avoltage control type regulator body 260. The dummy core capacities C areselectively connected to the output terminal by a PMOS transistor QP23which is controlled by a core selecting signal. Specifically, the dummycore capacities C are connected so that the load of the regulator iscoincident with the capacity when all of cores are selected.

By the above described control of the addition of the dummy corecapacities, it is possible to realize a predetermined power supplytransition regardless of the number of selected cores.

Specifically, assuming that the capacity of one core is C (core), thenumber of selected cores is m (select) and the total number of cores ism (total), the added dummy core capacity C (dummy) may be controlled soas to meet the following formula (1).

C(dummy)={m(total)−m(select)}·C(core)  (1)

(Tenth Preferred Embodiment)

FIG. 35 shows another preferred embodiment according to the firstmethod. In this preferred embodiment, a current addition type powersupply control circuit is similarly devised. A regulator body 280 is aknown regulator body, and utilizes a current addition system which usesan R/2R rudder circuit for monitoring the output voltage and a switch271 for switching the current path. Also in this case, by selectivelyconnecting dummy core capacities C to the output terminal of a regulator208, the load capacity is always the same as that when all of cores areselected, similar to the above described preferred embodiment.

Thus, it is possible to realize a predetermined power supply transitionregardless of the number of cores.

(Eleventh Preferred Embodiment)

FIG. 36 shows a preferred embodiment according to the second method. Aregulator 260 a basically has a voltage addition type regulator body 260shown in FIG. 34, and has driving PMOS transistors QP22 and NMOStransistors QN22 as a plurality of systems which are arranged inparallel. In each of these systems, switching PMOS transistors QP24 andNMOS transistors QN24 are inserted to be selectively controlled inaccordance with the state of core selection.

Specifically, assuming that the number of selected cores is m (select),the transistor size of a unit driver/load is W (unit), the transistorsize of a driver/load controlled in accordance with the number of coresis W (control), the control may be carried out so as to meetW(control)=m(select)·W(unit).

Thus, the switching of the driving capability of the power supplycircuit (specifically, the substantial switching of the transistor size)can be carried out in accordance with the number of selected cores torealize a predetermined power supply transition regardless of the numberof cores.

(Twelfth Preferred Embodiment)

FIG. 37 shows another preferred embodiment according to the secondmethod. A regulator 280 a basically has a current addition typeregulator body 280 shown in FIG. 35, and has load PMOS transistors QP22and driver NMOS transistors QN22 as a plurality of systems which arearranged in parallel. In each of these systems, switching PMOStransistors QP24 and NMOS transistors QN24 are inserted to beselectively on-off controlled in accordance with the state of coreselection.

Thus, similar to FIG. 36, the switching of the driving capability of thepower supply circuit can be carried out in accordance with the number ofselected cores to realize a predetermined power supply transitionregardless of the number of cores.

(Thirteenth Preferred Embodiment)

FIG. 38 shows a preferred embodiment as a modified embodiment of thepower supply line switching circuit shown in FIG. 30. In this preferredembodiment, the coincidence of the output of a busy output circuit 301with a core address signal is detected by an AND gate 302 to control apower supply line switch 16. In this case, as shown in FIG. 39, the busyoutput circuit 301 derives OR of all registers of each core blockregister 42 to output a busy output.

In the system in this preferred embodiment, the number of coresconnected to the writing/erasing power supply line 8 b is always one.Therefore, the capacity added to the writing/erasing power supply isalways constant, so that controllability of the writing/erasing powersupply (fluctuation in level in a short time) and stability (oscillationresistance) are excellent. On the other hand, the number of coresconnected to the reading power supply line is the number of all cores,or the number of cores, from which one core in a write/erase mode isremoved. Thus, the capacity added to the reading power supply issubstantially constant, so that the controllability and stability areexcellent.

(Fourteenth Preferred Embodiment)

A preferred control method for switching a reading power supply and awriting/erasing power supply will be described below.

In both of the free core system and the free bank system, only one setof reading power supply and power supply line, and only one set ofwriting/erasing power supply and power supply line are prepared in achip. Therefore, if the writing/erasing power supply is switched to thereading power supply when the data write or erase operation iscompleted, the fluctuation in power supply potential occurs due to theswitching. This state is shown in FIG. 40. When the data write/eraseoperation in core A and the data read operation in core B aresimultaneously carried out, if the operation of core A is completed toswitch the power supply, a bump is produced in the reading power supplypotential as shown in FIG. 40, so that there is the possibility that thefluctuation in power supply causes an access lag and the output of errordata in core B, in which a read operation is being carried out.

In order to prevent this, as shown in FIG. 41, the writing/erasing powersupply gives a power supply transition prior to switching so as to havethe same potential as the reading power supply when the selected core isswitched to the reading power supply. By carrying out such a switchingcontrol, it is possible to prevent the fluctuation in reading powersupply potential, and simultaneously, it is possible to preventmalfunction of a core, in which a read operation is being carried out.

(Fifteenth Preferred Embodiment)

A preferred embodiment of the efficient relationship between thearrangement of cell array blocks in cores and the arrangement of addressbus lines, data bus lines and power supply lines will be describedbelow. FIGS. 42 and 43 show examples of such preferred layouts.

When one core comprises n array blocks, one core comprise 1 row×ncolumns as shown in FIG. 42, or 2 rows×(n/2) columns as shown in FIG.43.

When one core comprises two rows as shown in FIG. 43, although there isan advantage in that local bus lines LB (including address lines, datalines and power supply lines) in cores can be commonly used for adjacentblocks, the layout area of common bus lines CB (including address lines,data lines and power supply lines) increases. In view of the wholelayout area, it is determined whether one-row or two-row construction isselected. If one core comprises three rows or more, the length of thecommon bus lines CB increases, so that the layout is not minimum.

When one core comprises two rows, if n is an odd number, the corecomprises 2 rows×[(n+1)/2] columns.

By arranging the common bus CB in each core in row directions and byarranging a switching circuit (an address line switch, a data lineswitch and a power supply line switch) in each core, the address, dataand power supply lines are arranged between the common bus CB and eachcore at the minimum distance, so that an efficient layout can beobtained. Moreover, by arranging the address line switch, the data lineswitch and the power supply line switch in row directions as a switchingcircuit for each core, the layout has a closer pattern. The localaddress line switch for each core is arranged in parallel to the commonbus lines CB, or below the common bus lines CB when a multi-layermetallization is used.

Comparing the core comprising one row in FIG. 42 with the corecomprising two rows in FIG. 43, the core comprising one row has longerlocal bus lines LB although it has a smaller layout of common bus linesCB and switching circuit.

On the basis of the length of the common bus lines CB plus the length ofthe local bus lines LB in the whole chip, it is determined whether theone-row construction or the two-row construction is selected. This pointwill be described in detail below.

Now, as shown in FIG. 1, it is assumed that the total number of cores ism (total), the number of blocks in one core is n, the length of oneblock in row directions is x (Block) and the length of one block incolumn directions is y (Block). Then, the length of the common bus lineCB plus the length of the local bus lines LB (one row) in the corecomprising one row is expressed by the following formula (2).

1(one row)=y(Block)×n×m(total)+x(Block)×m(total)  (2)

On the other hand, the length of the common bus lines CB plus the lengthof the local bus lines LB (two rows) in the core comprising two rows isexpressed by the following formula (3).

1(two rows)=(½)×y(Block)×n×m(total)+2×x(Block)×m(total)  (3)

The relationship in large and small between these cores is 1(onerow)<1(two rows) when (½)×n×y(Block)<x(Block). In this case, the corecomprising one row is advantageous. In the opposite case, the corecomprising two rows is advantageous.

However, the above described formulae are established when the number nof blocks is an even number. When the number n of blocks is an oddnumber, (n+1) may be substituted for n.

With the above described construction, it is possible to realize aclosest layout in a free bank system or a free core system.

(Sixteenth Preferred Embodiment)

FIG. 44 shows a preferred embodiment as a modified embodiment of theregulator power supply 260 a shown in FIG. 36. When a voltage VINTERdetected by registers R1, R2 connected to a power supply output terminalis fed back so that an internal power supply potential VINT has apredetermined control level, operational amplifiers OP1 and OP2 controlthe whole circuit so that VINTER=Vref. In the operational amplifiers OP1and OP2, diode connected transistors QN42 and QN43 provided for leakage.There are provided two drive circuits 401 and 402 having differentdriving capabilities for supplying current to a load capacity by acharging pump circuit output VCP on the basis of the current of acurrent source PMOS transistor QP41 controlled by the operationalamplifier OP1.

The PMOS transistors QP48 and QP40 of the drive circuits 401 and 402 areselectively connected to a node N3 of a current source, which iscontrolled by the operational amplifier OP1, or to the terminal of theboosted voltage VCP, by means of switching circuits 403 and 404. Thegates of the NMOS transistors QN46 and QN47 of the drive circuits 401and 402 are selectively connected to an output node N2 of theoperational amplifier OP2 or the ground potential by means of switchingcircuits 405 and 406.

The switching circuits 403 and 405 are controlled by a control signalSEL1 and a signal SEL1B which is complementary thereto. The switchingcircuits 404 and 406 are controlled by a control signal SEL2 and asignal SEL2B which is complementary thereto.

When the control signal SEL1=“H”, the PMOS transistor QP38 and NMOStransistor QN46 of the drive circuit 401 are controlled by the nodes N3and N2, respectively, so as to supply current from the voltage VCP tothe output terminal. When the control signal SEL2=“H”, the PMOStransistor QP49 and NMOS transistor QN47 of the drive circuit 402 arecontrolled by the nodes N3 and N2, respectively, so as to supply currentfrom the voltage VCP to the output terminal. In addition, if both of thecontrol signals SEL1 and SEL2 have “H”, both of the drive circuits 401and 402 can be activated.

For example, the driving capability of one drive circuit 401 is designedto be double the driving capability of the other drive circuit. Thesedrive circuits 401 and 402 are switched by the control signals SEL1 andSEL2 in accordance with the load capacity. That is, if the drive circuit402 is designed to be activated in an operation mode, in which the loadcapacity is small, and if the drive circuit 401 is designed to beactivated in an operation mode, in which the load capacity is large, itis possible to prevent the transition lag and oscillation of the powersupply potential.

Effectiveness in such a control for switching the driving capability ofa power supply will be described in detail below.

FIG. 45 shows the relationship between a ratio of a load capacity (c) todriving capability (W) of a power supply and a power supply transitiontime. Assuming that C/W capable of carrying out an earliest transitionis X, a transition lag occurs due to oscillation and so forth whenC/W<X. When C/W>X, a stable operation is carried out on a theoreticalstraight line wherein the transition time increases in proportion as theincrease of C/W. The reason why the transition time is gradually shiftedfrom the theoretical line as C/W approaches X is that it takes a lot oftime due to overshoot or undershoot of the internal power supply untilthe stable operation is carried out. In order to achieve the stabletransition of the internal power supply in a certain transition time T1or less, it must be set so that X<C/W<X1. Therefore, when the loadcapacity C has a plurality of different values, it is effective toswitch the driving capability W.

Specifically, in the power supply regulator of FIG. 44, when the controlsignal SELL has “H”, the load capacity is set to be double that when theSEL2 has “H”. In addition, it is assumed that only one drive circuitexists in FIG. 44, and it is assumed to set so that C/W=X1 in order toallow the driving capability to cause the power supply transition attime T1 on the basis of the load condition of the control signalSEL2=“H”. Then, under the load condition of the control signal SEL1=“H”,C/W is 2·X1, so that the transition time greatly exceeds a specifiedtransition time. Therefore, as described above, by preparing the drivecircuit 401 which is selected by the control signal SEL1 and which isseparate from the drive circuit 402 controlled by the control signalSEL2, and by setting the driving capability of the drive circuit 401 tobe double that of the drive circuit 402, it is possible to obtain thespecified transition time regardless of the load capacity.

This preferred embodiment is also effective against the fluctuation inexternal power supply level. FIG. 46 shows the relationship between C/Wof an internal power supply and a power supply transition time withrespect to different external power supply levels. That is, when theexternal power supply is low, C/W capable of carrying out the earliesttransition without causing oscillation is X, whereas when the externalpower supply increases, this C/W is X′. This means that even if the loadcapacity and driving capability of the internal power supply are thesame, when the external power supply is high, the capability of thedriving transistor is high to rapidly cause charge and discharge, sothat the internal power supply is easy to oscillate. In a case where thetransition of the internal power supply is intended to be caused in timeT1, when the external power supply is low, X<C/W<X1, whereas when theexternal power supply is high, X′<C/W<X1′, so that C/W slides toward ahigh value.

Therefore, when the driving capability is not designed to be variable,the driving capability and load must be set in the range of X′<C/W<X1 inorder to meet the condition of transition in the non-oscillated time T1,so that the allowable range of design is narrow. On the other hand, byswitching the driving capability as shown in FIG. 44, it is possible towiden the setting range. In this case, the output of an external powersupply detecting circuit and so forth are used as the control signalsSEL1 and SEL2.

(Seventeenth Preferred Embodiment)

In the above described preferred embodiments, flash memories have beenmainly described. As shown in FIG. 1, when a large number of cores arearranged in a large scale flash memory, data bus lines, address buslines and so forth, which are used commonly for each core, are usuallyarranged outside of the region of cores. The same layout is not utilizedonly for flash memories, but it is also utilized for varioussemiconductor integrated circuits wherein a plurality of functionalblocks are arranged. However, if the number of cores and functionalblocks increases, the area of the chip occupied by the region of buslines increases, so that the area penalty increases.

Therefore, a preferred embodiment capable of reducing such an areapenalty, thus, of reducing the chip size, is shown in FIG. 47. In FIG.47, a plurality of functional blocks BLKi (i=0˜3 in the case of theshown embodiment) are arranged in row (X) directions. The respectivefunctional blocks BLKi may be the same kind of memory core circuits asdescribed in the preceding preferred embodiments, or may be circuitsother than memory circuits, e.g., logical circuit blocks. That is, eachof the functional blocks BLKi is arranged as a set of certain circuitfunctions. In each of the functional blocks BLKi, signal lines 110 areformed for receiving and transmitting signals in and from the outside.

In this preferred embodiment, common bus lines 101 used commonly for therespective functional blocks BLKi are provided over the region of therespective functional blocks BLKi so as to extend over the respectivefunctional blocks BLKi in X directions. The signal lines 110 on theregion of the respective functional blocks BLKi are lines in a lowerlayer, and the common bus lines 101 are lines in an upper layer formedon the signal lines 110 via an interlayer insulator film. The common buslines 101 are connected to the signal lines 110 of the respectivefunctional blocks BLKi at suitable places by means of contacts 111.

By adopting such a layout, it is possible to reduce the chip size incomparison with the case where the region of common bus lines isprovided separately from the region of functional blocks BLKi. Inaddition, it is not required to arrange incoming lines for drawing thecommon bus lines into the respective functional blocks BLKi.

(Eighteenth Preferred Embodiment)

FIG. 48 shows a preferred embodiment wherein the same technique as thatin the above described seventeenth preferred embodiment is applied to aflash memory shown in FIG. 1. That is, cores constituting cell arrays ofa flash memory are arranged in X directions as those corresponding tofunctional blocks BLKi of FIG. 47. As a decoder circuit (correspondingto the matrix decoder 2 in FIG. 1), attached to each core, for decodingaddress signals, there are provided a pre-decoder 105 for selectingcores, and a row (X) decoder 103 and column (Y) decoder 104 for decodingan output decode signal of the pre-decoder 105 to select rows andcolumns.

In this preferred embodiment, common bus lines 102 commonly used in allof cores are provided continuously in X directions over the region ofthe pre-decoder 105 attached to each core.

Thus, it is possible to reduce the chip size in comparison with the casewhere the region of common bus lines is provided outside of the regionof cores. In addition, it is not required to arrange incoming lines fordrawing the common bus lines into each core region.

(Ninth Preferred Embodiment)

FIG. 49 shows a preferred embodiment as a modified embodiment of thepreferred embodiment of FIG. 48. In this preferred embodiment, cores arearranged in the form of a matrix. The adjacent cores in X directions areline-symmetrically arranged, and the adjacent cores in Y directions arealso line-symmetrically arranged on both sides of the X decoder 103 andthe pre-decoder 105. In the figure, F-shaped patterns show the symmetryof the layout. In FIG. 49, there are provided common bus lines 102 acommonly utilized for a plurality of cores (00, 01, 02, 03) in the upperportion in Y directions, and common bus lines 102 b commonly utilize fora plurality of cores (10, 11, 12, 13) in the lower portion.

In addition to the adoption of such a layout, adjacent cores share apart of a conductive type well region of a decoder circuit for theadjacent cores. That is, although the Y decoder 104 for adjacent coresin X directions has N wells for forming PMOS transistors, and P wellsfor forming NMOS transistors, the P or N wells, the P wells in theexample of FIG. 49, are integrally formed as a common P well withoutproviding any element isolating films therebetween. Similarly, thepre-decoder 105 for adjacent cores in Y directions shares the P wells ofthe P and N wells are shared.

Thus, by line-symmetrically arranging the cores in the form of thematrix and by sharing the wells of the decoder, area penalty can befurther reduced.

(Twentieth Preferred Embodiment)

While the common bus lines 102 a and 102 b have been provided separatelyfor the upper and lower cores in FIG. 49, these common bus lines 102 aand 102 b may be shared. A preferred embodiment of such a layout isshown in FIG. 50. In FIG. 50, pre-decoders 105 for upper and lower coresin Y directions are enlarged. Each of the pre-decoders 105 comprisesPMOS transistors QP and NMOS transistors QN which are formed in an Nwell 107 and a P well, respectively. As described above, the upper andlower pre-decoders 105 share the P well 106.

The common bus lines 102 shared by the upper and lower cores areprovided over the boundary region between the pre-decoders 105 for theupper and lower cores. The common bus lines 102 are formed as lines in alayer above the signal lines 108 provided in each of the pre-decoders105, and connected to the signal lines 108 via contacts at suitableplaces. In the shown example, the signal lines 108 are address signallines connected to the gates of the respective transistors of thepre-decoders 105. Therefore, the common bus lines 102 are also addressbus lines.

By thus sharing the common bus lines by the cores, it is possible toreduce current consumption in comparison with that in the preferredembodiment shown in FIG. 49.

(Twenty-First Preferred Embodiment)

FIGS. 51A and 51B show a preferred embodiment as a modified embodimentof the preferred embodiment of FIG. 49. In these figures, adjacent cores01 and 11 in Y directions in FIG. 49 are extracted. In FIG. 49, thepre-decoders 105 for the upper and lower cores in Y directions areadjacent in Y directions. On the other hand, in this preferredembodiment, the pre-decoders 105 for the upper and lower cores arearranged in X directions. If the area of two pre-decoders 105 for theupper and lower cores in FIG. 49 is not substantially changed, the areaof one pre-decoder 105 in the case of FIG. 51A has a size in Xdirection, which is about half of that in FIG. 49, and a size in Ydirection, which is about double that in FIG. 49.

In addition, in this preferred embodiment, transistors QP and QN of thepre-decoders 105 are arranged below common bus lines 102 as shown inFIG. 51B. In this case, the common bus lines 102 can be connecteddirectly to the gate electrodes 109 of the transistors via contacts.Thus, it is possible to further reduce area penalty.

However, in this preferred embodiment, the two pre-decoders 105 shown inFIG. 51Aa are not line-symmetrical in X directions, so that decodeoutput lines 201 from each of the pre-decoders 105 are extended in thesame X directions to enter the Y decoders 104 in the upper and lowercores. Therefore, the decode output lines 201 are concentrated in theinput part to the Y decoders 104.

(Twenty-Second Preferred Embodiment)

FIGS. 52A and 52B show a preferred embodiment wherein the concentrationof the decode output lines 201 in the preferred embodiment shown inFIGS. 51A and 51B is avoided. In this preferred embodiment, thepre-decoders 105 in the upper and lower cores in the preferredembodiment shown in FIGS. 51A and 51B are arranged line-symmetrically inX directions, and the body parts and Y decoders 104 in the upper andlower cores are arranged rotation-symmetrically.

As shown in FIG. 52A, the decode output lines 201 of each of the Ydecoders 105 are extended on both sides in X directions to enter the Ydecoders 104. Therefore, in comparison with the preferred embodimentshown in FIGS. 51A and 51B, the concentration of the lines in the Ydecoders 104 is relieved, so that it is possible to reduce area penalty.

(Twenty-Third Preferred Embodiment)

A preferred embodiment wherein the technique for providing the commonbus lines in the preferred embodiment shown in FIGS. 52A and 52B isapplied to a flash memory of a redundant circuit system will bedescribed below.

In a flash memory using nonvolatile memory cells having a stacked gatestructure for electrically writing/erasing data by utilizing tunnelcurrent, if in a block serving a unit of batch erase has even onedefective row wherein a word line is short-circuited with a channel, theblock is defective. Because the erase voltage during data erase is notapplied to the whole block due to the short-circuit of the single wordline. Therefore, in order to cope with such a defect, a redundant blockis provided for using a block redundancy for relieving a defect.

In order to realize the block redundancy when a core comprising a set ofa plurality of blocks as described in the first preferred embodiment, anindividual decoder circuit is preferably provided without attaching theredundant block to the core so that the redundant block can be replacedwith an optional block in the core. A preferred embodiment of a layouthaving such a redundant block is shown in FIG. 53.

FIG. 53 shows two cores, each of which comprises a plurality of blocks.A redundant block 301 is provided with an X decoder 301 and a Y decoder303, which are independent of the cores as described above, and apre-decoder 304 at the front stage thereof. In addition, a pre-decoder105 for the core body, and the pre-decoder 303 of the redundant block301 are arranged by the same layout as the relationship between the twopre-decoders of the upper and lower cores in the preceding preferredembodiment shown in FIGS. 52A and 52B.

That is, the pre-decoder 105 on the core side and the pre-decoder 304 onthe redundant block 301 side are arranged in a region between the bodycore and the redundant block 301 so as to be line-symmetric in Xdirections. In addition, on the region of the pre-decoders 105 and 304,a common bus line 305 is provided continuously in X directions. Similarto the twenty-second preferred embodiment, the common bus line 305 isconnected to the input signal lines of the respective pre-decoder 105and 304 via contacts. Similar to the case of FIG. 52A, the decode outputlines 201 and 306 of the respective pre-decoders 105 and 304 aredistributed to be connected to the Y decoders 104 and 303 of the coreand the redundant block 301, respectively.

Thus, also in the flash memory of the redundant circuit system, it ispossible to effectively reduce area penalty by taking account of thearrangement of the common bus line.

(Twenty-Fourth Preferred Embodiment)

A preferred embodiment of a sense amplifier according to the presentinvention, which is applied to a flash memory capable of simultaneouslycarrying out a data write/erase operation and a data read operation inthe first preferred embodiment, will be described below.

Usually, a data read system used for a flash memory of this type isformed as shown in FIG. 54. A data line DL selected from a cell array401 by a column gate 402 enters one input terminal of a data comparatorcircuit 403. A reference data line REF connected to the other inputterminal of the data comparator circuit 403 is connected to a constantcurrent source 405 via a dummy column gate 404. Thus, by comparing thecurrent of the data line DL with the current of the reference data lineREF, data “0” or “1” is determined.

For example, it is assumed that a flat memory is a NOR type flashmemory. Then, as shown in FIG. 56, electrons are accumulated in afloating gate FG of a memory cell by the hot electron injection from thedrain side, so that the memory cell is in a high threshold voltage state(e.g., “0” state). In addition, by discharging the electrons of thefloating gate FG to the channel side, the memory cell is in a lowthreshold voltage state (e.g., “1” state). By comparing and detectingthe presence of the drawing of current due to the difference between thethreshold voltages, by means of the data comparator circuit 403, dataare discriminated. For example, the data comparator circuit 403 mainlycomprises a CMOS differential amplifier DA as shown in FIG. 55.

Although a verify read operation for verifying a write or erase state iscarried out in a data write/erase operation, a constant current sourcegenerally used for the verify read operation can be common to that usedfor a usual data read operation. However, in a flash memory capable ofsimultaneously carrying out a data write/erase operation and a data readoperation, a usual data read operation and a verify read operation areasynchronously carried out. In this case, since it is required to carryout data line equalization, it is difficult to share the constantcurrent source. The data line equalization means to short-circuit thedata line DL and reference data line REF, which are shown in FIG. 54, toinitialize these lines in the same potential state in order toaccelerate a data read operation.

Therefore, usually, constant current sources for a usual data readsystem and a verify read system are separately prepared. This causesanother problem. That is, if there is dispersion in the respectiveconstant current sources, a threshold voltage for a memory cell detectedby a verify read operation is different from a threshold voltagedetected by a usual read operation, so that error read is caused.

Therefore, in this preferred embodiment, a read system configuration isformed so that the constant current source for the usual read operationand the constant current source for the verify read operation have thesame current value. This read system configuration is shown in FIG. 57.This figure shows read systems of two cores, core 0 in a datawrite/erase mode and core 1 in a data read mode. The bit lines of thememory cell arrays 401 a and 401 b of the respective cores are selectedby column gates 402 a and 402 b, respectively. The output of each systemis optionally switched by a data line switch 407. The effective datalines DLa and DLb selected by the data line switch 407 enter datacomparator circuits 403 a and 403 b, respectively. The reference signallines REFa and REFb of the respective data comparator circuits 403 a and403 b are connected to a common constant current source 406 via dummycolumn gates 404 a and 404 b, respectively.

The constant current source 406 is formed as shown in FIG. 58. Areference constant current source 501 has a PMOS current mirror using apair of PMOS transistors QP1 and QP2, a reference current sourcetransistor TO connected to the PMOS transistor QP1 via a switching NMOStransistor QN1, and an NMOS transistor QN3 connected to the PMOStransistor QP2 via a switching NMOS transistor QN2. The NMOS transistorsQN1 and QN2 are driven by a control signal SW to control the activationand deactivation of the reference constant current source 501. The NMOStransistor QN3 is diode-connected via the NMOS transistor QN2.

The current I0 passing through the reference current source transistorT0 is a reference current. If the PMOS transistors QP1 and QP2 are thesame element parameter, the reference current I0 passes through the NMOStransistor QN3 by the function of the PMOS current mirror. In addition,there are provided two current source NMOS transistors T1 and T2 whichare driven in parallel by the potential of the output node N of thereference constant current source 501 determined by the referencecurrent I0. These two NMOS transistors T1 and T2 have the same elementparameter, and the drains thereof are connected to reference signallines REFa and REFb, respectively.

Thus, since the same current pass through the current source transistorsT1 and T2, even if the set current value is shifted, the current valuesof the reference signal lines REFa and REFb in the usual read operationand the verify read operation are always the same, so that it ispossible to obtain a high read margin.

In this preferred embodiment, the reference current source transistor T0of the reference current source 501 is preferably an electricallyrewritable nonvolatile memory cell which is the same as a nonvolatilememory cell used for a memory cell array. In this case, by rewriting thereference current source transistor T0, the reference current value I0can be changed, so that the current values of the reference signal linesREFa and REFb can be change. Thus, even if the reference current valueI0 is changed, the current values of the reference signal lines REFa andREFb are the same values.

As described above, according to this preferred embodiment, the currentpassing through the reference signal lines of the usual read system andverify read system can be always maintained at the same value, so thatit is possible to surely prevent the deterioration of the read marginand error read.

As described above, according to the present invention, it is possibleto obtain a flash memory of a free core system wherein a memory cellarray comprises a plurality of cores, each of which comprises one blockor a set of a plurality of blocks, each of which constitutes an eraseunit of a flash memory, and an optional core can be selected to executea data write or erase operation while executing a data read operation inanother optional core. Unlike conventional flash memories, the range ofsimultaneously executing a data write or erase operation and a data readoperation is not fixed, so that it is possible to obtain a flash memoryhaving a high degree of freedom.

In addition, according to the present invention, an optionally selectedcore is used as a first bank and the rest of cores is a second bank bymeans of a bank setting memory circuit, so that it is possible to obtaina flash memory of a free bank system capable of optionally setting thebank size. Thus, while a data write or erase operation is carried out inan optional block in the first bank, a data read operation can becarried out in the second bank.

While the present invention has been disclosed in terms of the preferredembodiment in order to facilitate better understanding thereof, itshould be appreciated that the invention can be embodied in various wayswithout departing from the principle of the invention. Therefore, theinvention should be understood to include all possible embodiments andmodification to the shown embodiments which can be embodied withoutdeparting from the principle of the invention as set forth in theappended claims.

What is claimed is:
 1. A semiconductor device comprising: a memory cellarray having the arrangement of a plurality of cores, each of whichcomprises one block or a set of a plurality of blocks, each blockdefining a range of memory cells serving as a unit of data erase, eachof said memory cells being an electrically rewritable nonvolatile memorycell; a core selecting portion configured to select an optional numberof cores from said plurality of cores for writing, erasing or readingdata; and a power supply control circuit detecting an internal powersupply voltage to hold a transition in the internal power supply voltageat a predetermined level, the power supply control circuit having aplurality of dummy load capacitors selectively connected in accordancewith the number of cores selected by the core selecting portion.
 2. Thenonvolatile semiconductor memory device as set forth in claim 1, whereinsaid power supply control circuit detects an external power supplyvoltage to generate a detection signal and changes said dummy loadcapacity, which is to be connected, on the basis of said signal.
 3. Asemiconductor device comprising: a memory cell array having thearrangement of a plurality of cores, each of which comprises one blockor a set of a plurality of blocks, each block defining a range of memorycells serving as a unit of data erase, each of said memory cells beingan electrically rewritable nonvolatile memory cell; a core selectingportion configured to select an optional number of cores from saidplurality of cores for writing, erasing or reading data; and a powersupply control circuit detecting an internal power supply voltage tohold a transition in the internal power supply voltage at apredetermined level, the rower supply control circuit having a circuitchanging an internal power supply driving capability in accordance withthe number of cores selected by the core selection portion.
 4. Thenonvolatile semiconductor memory device as set forth in claim 3, whereinsaid power supply control circuit detects an external power supplyvoltage to generate a detection signal and changes said internal powersupply driving capability on the basis of said detection signal.